1. Field of the Invention
This invention relates to viewfinder indicating devices for cameras, for indicating shutter speed to provide proper exposure in accordance with the intensity of light from an object, the set film sensitivity, a preset f-number, or for indicating an f-number for providing a proper exposure in accordance with the intensity of the light, the set film sensitivity and a preselected shutter speed.
2. Prior Art
Prior art automatic exposure controls for cameras adopt either a diaphragm-priority, automatic shutter speed control system or a shutter-speed-priority, automatic diaphragm control system. In the former type, a shutter speed to be automatically controlled is indicated, and in the latter type, an f-number to be automatically controlled is indicated. Whether the f-number or the shutter speed is set by priority is largely dependent on the photographing conditions or the operator's will. A demand therefore arises for the capability of setting an f-number by priority as well as setting a shutter speed by priority in a single camera.
To meet the above demand, in designing a viewfinder indicating device for a camera which is capable of setting the f-number and setting the shutter speed by priority, the ordinary mechanism provides a shutter speed scale and a separate f-number scale which can be seen within a viewfinder; an indicating means operable according to a preset f-number and the value of light measured; and an indicating means operable according to a preset shutter speed and the value of light measured. The latter two means are disposed in opposing relation to the shutter speed scale and f-number scale, respectively. Arrangements employing such a dual indicating means result in increased manufacturing cost and increased space for mounting such means. Furthermore, the provision of the shutter speed scale and the f-number scale which may be simultaneously seen within the viewfinder causes the operator to be momentarily confused in judging which one of the scales is to be read.
The viewfinder indicating device desclosed in U.S. Pat. No. 3,829,867 attempts to solve the problems described, and is applied to an automatic exposure control, T.T.L. light measuring single lens reflex camera, wherein two exposure modes, such as shutter-speed priority, automatic diaphragm control and diaphragm priority, automatic shutter speed control, are alternatively selectable. The viewfinder indicating device disclosed in the aforesaid patent is so arranged that a first indicating member having a shutter speed scale thereon and a second indicating member having an f-number scale thereon are shifted in opposite directions in accordance with the selected control mode. Thus, when automatic shutter speed control is selected, only the shutter speed scale is within the viewfinder optical path. Conversely, when automatic f-number control is selected, only the f-number scale is within the viewfinder optical path. Also, only a single meter is used as a means for indicating both the shutter speed and the f-number. With such an indicating device, a meter used as an indicating means is susceptible to vibration, and the provision of two indicating members for the shutter speed scale and for the f-number scale, respectively, requires a complex mechanism to shift the indicating members. Furthermore, irrespective of whether the signal to the meter is an f-number signal or a shutter speed signal, the signal to oscillate the meter pointer to a given degree must be maintained constant. For this reason, the f-number scale and the shutter speed scale must be maintained in a constant positional relationship. To this end, adjustment of the positional relationship between these two indicating members is unavoidable upon assembly.